Thursday, 22 December 2011

Class 8 - Science - CH10 - Reaching Age of Adolescence

(NCERT Solutions) Q1: What is the term used for secretions of endocrine glands responsible for changes taking place in the body?

Answer: Hormones. Hormones are chemical messengers that transport signal from one cell(or gland) to another cell (or gland).

Q2: Define adolescence.

Answer: The period of life, when the body undergoes changes, leading to reproductive maturity, is called adolescence. Adolescence begins around the age of 11 and lasts upto 18 or 19 years of age. Since this period covers the ‘teens’ (13 to 18 or 19 years of age), adolescents are also called ‘teenagers’. In girls, adolescence may begin a year or two earlier than in boys. Also, the period of adolescence varies from person to person.

Q3: What is menstruation? Explain.

Answer: In a female reproductive ovaries, the ova begin to mature with the onset of puberty. One ovum matures and is released by one of the ovaries once in about 28 to 30 days. During this period, the wall of the uterus becomes thick so as to receive the egg, in case it is fertilized and begins to develop. If fertilization does not occur, the released egg, and the thickened lining of the uterus along with its blood vessels are shed off. This causes bleeding in women which is called menstruation. Menstruation occurs once in about 28 to 30 days.

Changes in Boys during puberty:
1. Facial hairs such as beard and moustaches develop.
2. Hair develops under the armpit, under chest and in the pubic regions.
3. Voice becomes deeper.
4. Muscles develop, and shoulder becomes broad.
5. Increase in weight.

Changes in Girls during puberty:
1. Development and enlargement of breasts.
2. Hair develops under the armpit and in the pubic regions.
3. Hips broaden and pelvic region widens
4. Initiation of menstrual cycle.
5. Deposition of fat around hips,

Q5: Prepare a Table having two columns depicting names of endocrine glands and hormones secreted by them.

Answer:

Endocrine Glands

Hormones secreted

i. Pituitary

Growth Hormones

ii. Thyroid

Thyroxine

iii. Adrenal Glands

Adrenalin

iv Pancreas

Insulin

v. Testes

Testosterone

vi. Ovaries

Estrogen, Progestrone

Q6: What are sex hormones? Why are they named so? State their function.

Answer: Hormones which constitute the secondary sexual characters are called sex hormones.

In general, hormones work instantly when they released in blood stream. Sex hormones
are different because they start to work later on. They gradually prepare the body for reproduction.
The sex hormones are responsible for the fundamental change in growth and development and stimulate the developments of secondary sexual characters. The testes and the ovaries are the reproductive Organs; and both are stimulated by the pituitary hormone during Puberty. That's the reason these are called sex hormones.

Functions of Sex Hormones:
1. In male, the testes produces the male sex hormone testosterone. This hormone helps in the development and maintenance of the primary and secondary sexual characters and functions of sperms.

2. In female, the ovaries secrete estrogen and progesterone responsible for the primary and secondary sexual characters.

Q7: Choose the correct option.

(a) Adolescents should be careful about what they eat, because
(i) proper diet develops their brains.
(ii) proper diet is needed for the rapid growth taking place in their body.
(iii) adolescents feel hungry all the time.
(iv) taste buds are well developed in teenagers.

Answer (ii) proper diet is needed for the rapid growth taking place in their body.

Answer:(a) Adam's apple: The protruding part of the throat is called Adam’s apple. It is the enlarged voice box or larynx which gets enlarged and visible from outside in boys at the onset of puberty. This makes the voice of boys hoarse.

(b) Secondary Sexual Characters are those characters which distinguish a male from female. A few of these are described below:

Girls:
1. Development and enlargement of breasts.
2. Hair develops under the armpit and in the pubic regions.
3. Hips broaden and pelvic region widens
4. Initiation of menstrual cycle.
5. Deposition of fat around hips,

(c) Sex determination in unborn baby: All human beings have 23 pairs of chromosomes in the nuclei of their cells. Two chromosomes out of these are the sex chromosomes, named X and Y. A female has two X chromosomes, while a male has one X and one Y chromosome. The gametes (egg and sperm) have only one set of chromosomes. The unfertilised egg always has one X chromosome.But sperms are of two kinds. One kind has an X chromosome, and the other kind has a Y chromosome. When a sperm
containing X chromosome fertilises the egg, the zygote would have two X chromosomes and develop into a female child. If the sperm contributes a Y chromosome to the egg (ovum) at fertilisation, the zygote would develop into a male child. This concludes that the sex chromosomes of the father determine the sex of an unborn baby.

Q10. The table below shows the data on likely heights of boys and girls as they grow in age. Draw graphs showing height and age for both boys and girls on the same graph paper. What conclusions can be drawn from these graphs?

Answer: Conclusion:
(i) Girls are taller than boys till they reach the age of 12 years.
(ii) Till the age of 16 years, the heigh of both boys and girls remain the same.
(iii) After 16, both boys and girls gain increase in height. In general, boys are taller than girls.

Q11: Why do personal hygiene become more important during adolescent age?

Answer: The basic aim of personal hygiene is to keep body neat and clean and to avoid microbes like bacteria, virus entering our body. Otherwise these harmful bodies can infect us.

Q12: What precautions should be taken to maintain personal hygeine?

Answer: To maintain personal hygiene following precautions must be taken:

Before and after taking meals, always wash your hands with tap water.

Take bath regularly with clean water.

Brush your teeth after each meal and before going to bed to avoid tooth decay.